Nitric oxide (NO), generated by nitric oxide synthases, is a key regulator of vascular tone. Recently, a fundamentally different pathway for NO production was described in which nitrate and nitrite are converted to NO and other bioactive nitrogen oxides. Research conducted during the last years has changed our way of viewing these anions, since nitrate and nitrite were long known predominantly as inert oxidative end products of NO metabolism. Plasma nitrate and nitrite do not only reflect the endogenous NOS activity since dietary sources of nitrate have a major impact of the circulating levels of these anions. Nitrate is abundant in our diet, and particularly high levels are found in many vegetables. After ingestion and absorption, circulating nitrate is actively taken up and concentrated in the salivary glands. When the nitrate-rich saliva is secreted into the oral cavity, nitrate reducing bacteria on the tongue reduce some of the nitrate to nitrite. Therefore, intake of nitrate-rich vegetables results in elevated plasma levels of both nitrate and nitrite. More recent, focus has been directed towards the role of nitrate intake and plasma nitrite in the control of blood pressure. In fact, there are now results showing that acute nitrate intake reduces blood pressure in humans, and also that nitrate intake over a longer period lowers blood pressure in animals. A diet rich in fruits and vegetables has been shown to reduce blood pressure and increased nitrate intake may be one of the explanations for this. Another fascinating aspect is revealed, since humans are dependent on the oral microflora for conversion of nitrate to nitrite, highlighting the importance of symbiosis between us and our microbes.